The monosaccharide transport system of the human erythrocyte has recently been purified. We propose to elucidate, at the molecular level, the structure, function, and mechanism of this transport system. The investigation of structure will include: analyses of carbohydrate and aminoacid composition; determination of the molecular weight and subunit (oligomeric) structure; delineation of the folding of the polypeptide chain relative to the plane of the membrane; the labeling of the active sites for monosaccharides and cytochalasin B; and the initiation of aminoacid sequence determination. Aspects of the function that will be examined are: transport activity upon incorporation into phospholipid vesicles; the stoichiometry of cytochalasin B binding; and the effects of lipid structure, including the type of phospholipid head groups, asymmetric distribution of lipid types across the membrane, and the phase state of fatty acyl residues, upon transport activity. The study of the mechanism of action of the purified transport system will be directed toward establishing the kinetic mechanism through examination of transient processes by the stopped-flow method. Individual steps will be recognized, and the values of rate and equilibrium constants for them will be obtained. In addition, a new purification method in which the transport system is isolated by affinity chromatography will be developed. Also, attempts will be made to increase the rate of sugar transport into intact cells by membrane fusion between their plasma membranes and phospholipid vesicles containing the purified transporter.